SPOILERS FOR NEAR THE ENDING OF BLOODBORNE
After killing Rom and starting the Blood Moon phase, if you enter Iosefka's Clinic from the back you can find her crouched on all fours on a stretcher. She is not hostile, and if you talk to her she says (among other things): "It's progressing... I can see things... I knew it, I'm different. I'm no beast... I... Oh... God, it feels awful... but, it proves that I'm chosen. Don't you see? How they writhe, writhe inside my head... It's... rather... rapturous..." If you attack her she drops a One Third of Umbilical Cord, suggesting she used her depraved experiments to impregnate herself with an infant Great One.
Of course, the game's character model doesn't reflect a rapidly progressing pregnancy, but that's what I'M here for! Nyahahahaha!